DictionaryspontaneousUnplanned or unprompted
adjective

spontaneous

spahn-TAY-nee-uhs/spɑːnˈteɪniəs/

Happening naturally without planning or outside prompting.

The spontaneous dance interrupts an ordinary walk home.

An impromptu dance interrupts an ordinary walk home: a compact two-moment sequence contrasts two women carrying groceries with one suddenly twirling and inviting her surprised companion to join.
Etymology

The Latin adjective meant acting of one's own free will. English extended this idea to actions and events arising from an internal impulse rather than external prompting; the underlying word for will has uncertain origins.

In context

Olympus Group12:59
prop usage can be spontaneous or can be pre-planned using a prop in a manner other than intended is one of the best ways to get a laugh
How to Perform in Your Mascot Costume from Olympus

More examples

  • They made a spontaneous trip to the beach.
  • Her laughter was warm and spontaneous.
  • The scientist recorded spontaneous changes in the sample.

Forms

spontaneous

spontaneity noun — natural action without planning

spontaneously adverb — without planning or prompting

Similar words

unplanned
Not arranged beforehand, without necessarily arising naturally.
impulsive
Done on a sudden urge, sometimes without enough thought.